A typical conveyor belt is fitted for running in a circle between a drive pulley and an idler pulley in an endless fashion. The belt conveys a conveying material in a forward direction, discharges the conveying material, and then returns on the pulley in a backward direction opposite to the forward direction. In this specification, a "forward path" refers to one portion of the travel of the conveyor belt through which the belt conveys the conveying material until discharging the material therefrom, and a "return path" refers to the rest portion of the travel through which the belt returns subsequent to the dropping of the conveying material. The return path thus includes a passage on the pulley immediately subsequent to a point of return.
Leavings remain stuck on the surface of the conveyor belt even after the dropping of the conveying material at the point of return, and a belt cleaner is thus arranged to remove the leavings stuck on the belt on the return path. As disclosed in U.S. Pat. No. 3,841,470, a conventional belt cleaner includes a plurality of cleaner units arranged in the transverse direction of the conveyor belt on the return path of the belt. These cleaner units are arranged on a support frame and are composed of scraping portions aligned in a line across the width of the belt on the return path and maintained in contact with the belt surface. Each cleaner unit has a scraper with a scraping portion having a tip on the top end thereof and a resilient member formed such as a rubber block for supporting the scraper. The cleaner units are adjusted for a vertical shift by the support frame so that the scraping portions on the top are aligned at the same level in height. By raising the support frame, the scraping portions are brought into contact with the belt surface by the resilient deformation of the resilient member and thereby scrape the leavings off the belt surface.
The leavings on the belt surface have irregular shapes such as wavy shapes, rather than having flat surfaces, and such irregularities appear not only in the longitudinal direction of the belt but also in the transverse direction of the belt. Since each cleaner unit resiliently supports its scraper by the corresponding resilient member as already discussed, each scraper may recede or advance independently between the cleaner units, following the irregularity of the leavings and thereby scraping the leavings off. When the irregularity of the leavings is large in height, or when the leavings are rigid at the peak thereof, the scraper in the course of scraping action recedes by means of the resilient member and passes over the peak. At the same time, the belt jumps or vibrates to recede from the scraper. When the belt vibrates in this way, the belt along the entire width thereof tends to lift from the scraper and the scraper's effect of scraping the leavings reduces in performance. Specifically, the pressing force of the scraper increases against the belt surface at the peaks of the leavings, while the pressing forces of the other scrapers in the rest of the belt surface weaken. The scraping portions of the linearly aligned scrapers fail to be pressed in uniform pressure against the belt surface, thereby causing non-uniformity in the scraping effect to the leavings in the transverse direction of the belt.
To reliably convey the conveying material thereon, the conveyor belt is generally supported by guide pulleys, arranged in a "trough" angle maintained with each other, so that the belt becomes arcuate in cross section. The leavings on the belt surface are thus large in the central portion of the belt and become smaller near at it goes to both sides of the belt, and the amount of leavings to be scraped by the scrapers is varied accordingly. For this reason, the linearly aligned scrapers wear more on the central scraping portions thereof than on the distal scraping portions thereof, thereby suffering from a biased abrasion. Since the resilient force of the resilient member exerting on the scraper varies in response to the amount of wear of the scraping portion (i.e., the more amount of wear, the less the resilient force of the scraping portion becomes), there occurs a difference in the pressure of the scraping portions against the belt surface between the array of scrapers subsequent to the creation of the biased abrasion. In other words, the scraping portions of the linearly aligned scrapers are unable to press against the belt surface in uniform pressure, and the scraping effect to the leavings is subject to non-uniformity across the width of the belt.
As a result of the conveyance operation of the conveyor belt and the scraping action by the belt cleaner, the conveyor belt itself suffers from wear on the belt surface. Also the conveyor belt is subject to a deformed shape due to its acquired "trough shaping habit" as mentioned above. In the conventional belt cleaner, the linearly aligned scrapers are not always uniformly pressed against the belt surface, thereby failing to achieve a uniform scraping effect across the width of the belt.